Tape guiding and transducing apparatus



Oct. 19, 1965 R. F. PFOST TAPE GUIDING AND TRANSDUCING APPARATUSOriginal Filed Oct. 11, 1957 4 Sheets-Sheet l A TTORNEYJ Oct. 19, 1965R. F. PFOST 3,213,205

TAPE GUIDING AND TRANSDUCING APPARATUS Original Filed Oct. 11, 1957 4Sheets-Sheet 2 F1EI E FIE EI INVENTOR. FOJf/KT fi PFOS'T WMZ/MW ATTOR/VEY5 Oct. 19, 1965 R. F. PFOST 3,213,205

TAPE GUIDING AND TRANSDUCING APPARATUS Original Filed Oct. 11, 1957 4Sheets-Sheet 5 ATTORNE Yf Oct. 19, 1965 R. F. PFOST TAPE GUIDING ANDTRANSDUCING APPARATUS 4 Sheets-Sheet 4 Original Filed Oct. 11, 1957INVENTOR. POBFPT/FPFOJT 81'770114144 United States Patent 3,213,205 TAPEGUIDING AND TRANSDUCING APPARATUS Robert F. Pfost, Mountain View,Calif., assignor to Ampex Corporation, Redwood City, Calif., acorporation of California Original application Oct. 11, 1957, Ser. No.689,594, new Patent No. 3,020,359, dated Feb. 6, 1962. Divided and thisapplication Oct. 16, 1961, Ser. No. 145,410

Claims. '(Cl. 179100.2)

This is a division of application Serial No. 689,594, filed October 11,1957, now U.S. Patent No. 3,020,359, issued February 6, 1962.

This invention relates generally to transducing apparatus making use ofa pliable tapelike record medium. It is applicable for recording and/orreproducing signal intelligence over a wide frequency spectrum,including for example video frequencies.

In US. Patents 2,956,114 and 2,916,546 there are disclosed systems andapparatus making use of a rotary head assembly for recording and/ orreproducing signals over a wide frequency spectrum. One practical usefor such a system is the recording and/or reproduction of televisionprograms. The head assembly employed comprises a plurality of transducerunits that are mounted to rotate and sweep across a pliable tapelikerecord medium, such as a magnetic tape. Special means are employed fordriving the head assembly and the magnetic tape to insure proper controlof the speed of rotation of the head and tape speed across the head, andto insure proper tracking during playback.

Systems of the above type necessarily involve separate recorded trackportions extending across the tape, each track portion being formed bythe sweep of a transducer unit. During playback, current Variationsprovided by each unit as it sweeps across a track portion are combinedin an electronic circuit to form a composite signal. With referenceparticularly to broad band (e.g. video) applications, the accuracy withwhich the signal is recorded and reproduced is dependent among otherthings upon the mechanical accuracy with which the rotary head isconstructed. Slight differences in the angular spacing between the tipsof the transducer units cause inaccuracies in the reproduced compositesignal. Assuming the reproduction of recorded video signals on a screen,such inaccuracies are evidenced by horizontal shifting betweenhorizontal bands of the picture.

One arrangement serving to compensate for such mechanical inaccuraciesemploys delay lines in the connections to the several transducer units,as disclosed in US. Patent No. 2,921,990. However delay lines requireadditional circuitry which adds considerably to the cost andcomplications of the system. Also if the same equipment is to be usedfor both recording and playback operations, separate delay lines must beused in each instance.

A further problem involved in the construction and operation of suchhead assemblies is that relatively high speeds of rotation are requiredwhereby the transducer units and associated parts are subjected toconsiderable centrifugal force. The head assembly should be constructedin such a manner that inaccuracies do not develop in usage, other thansuch inaccuracies as may be inherent in gradual wear of the transducerunits. The structural features of such a head assembly should inaddition permit a high degree of precision at the time of manufacturewithout undue expense. The size of the individual units must berelatively small, while transducing efficiency should be relatively highover the frequency range for which the apparatus is to be used.

Aside from the foregoing, various problems are involved ice in theconstruction of the complete transducing apparatus, including themounting of the tape guide whereby it can be shifted and adjustedrelative to the head.

In general it is an object of the present invention to provide a rotaryhead assembly of the above character which makes possible accurateangular spacing of the transducer units, thus avoiding the use of delaylines.

Another object is to provide a head assembly of the above characterwhich is constructed in such a manner as to provide simple adjustmentsfor precise location of the transducer units.

Another object is to provide a head assembly which will retain itsadjustment during normal usage.

Another object is to provide a head assembly having novel transducerunits that are effective over a wide range of signal frequencies, andwhich employ core materials of high magnetic permeability, such asferrite.

Another object of the invention is to provide a novel transducerapparatus including a rotary head and tape guiding means, and whichmakes possible free movement of the tape during fast forward or rewindoperations, and accurate presentation of the tape for contact with thetransducer units.

Another object of the invention is to provide a novel transducerapparatus of the above character which makes possible precise adjustmentof the contact pressure between the tape and the tips of the transducerunits.

Another object of the invention is to provide such apparatus with guidemeans readily removable from the other parts of the machine.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments have been setforth in detail in conjunction with the accompanying drawing.

Referering to the drawing:

FIGURE 1 is a plan view partly in section illustrating transducingapparatus incorporating the invention.

FIGURE 2 is a side elevational view partly in section illustrating theapparatus of FIGURE 1.

FIGURE 3 is an end view looking toward the right hand end of FIGURE 1and partly in section.

FIGURE 4 is a cross sectional view taken along the line 4-4 of FIGURE 1on an enlarged scale.

FIGURE 5 is a detail illustrating the motive means for moving the tapeguide and taken along the line 55 of FIGURE 1 (scale enlarged).

FIGURE 6 is detail showing the rotary head with the motor shaft shown insection and with the parts broken away.

FIGURE 7 is a side elevation of the head shown in FIGURE 6, taken alongline 77 of FIGURE 6, but with parts broken away to show one of theadjusting screws.

FIGURE 8 is a cross sectional detail on an enlarged scale taken alongthe line 8-8 of FIGURE 6.

FIGURE 9 is a cross sectional detail taken along the line 99 of FIGURE8.

FIGURE 10 is a detail illustrating the pole pieces and associated partsof one of the transducer units and illustrating the manner in which thepole tips protrude from the periphery of the head.

FIGURE 11 is a detail on the same scale as FIGURE 6 showing a portion ofthe head looking toward the rear side of FIGURE 6 and illustrating thetips of one of the transducer units.

FIGURE 12 is a detail taken along the line 1212 of FIGURE 8 and showingthe manner in which the pole pieces are carried on the inner side of themounting element.

FIGURE 13 is a schematic view illustrating the transducer apparatus inconjunction with other parts of a complete tape transport.

The apparatus illustrated particularly in FIGURE 1, 2 and 3 consists ofa head assembly 10, driven by an electric motor 11. As will be presentlyexplained, the head assembly includes a plurality of transducer unitsfor contact with the tape. Along one side of the head assembly there isa tape guide 12, which is adapted to present the tape to the rotary headassembly. A suitable base plate 13 serves to carry the operating parts,and can be mounted on the top plate or panel of the complete machine.

The preferred construction for the head assembly is shown in FIGURES 6to 12 inclusive. It consists of a member 16 which is circular in form,and formed of suitable rigid metal or metal alloy. The central opening17 serves to accommodate the motor shaft 18. A plurality of smalltransducer units, four in this instance, are mounted upon the member 16in such a manner that their operating tips protrude from the peripheryof the assembly. Each such unit consists of a magnetic core 21 made ofmaterial having a low core loss, such as ferrite. In the formillustrated in FIGURE 6, each core is annular with the polar ends of thebranches 22 spaced apart. A coil or winding 23 is provided on each core.Each magnetic core is associated with a pair of pole pieces 24 formed ofmetal or metal alloy of high magnetic permeaability, and preferablyhaving a hardness capable of withstanding wear occasioned by contact ofthe pole pieces with the tape. For example, these parts can be made ofAlfenol, which is a metal alloy having high magnetic permeability withrelatively good hardness and wear-resisting properties. The tip ends 26of these pole pieces, which contact the tape, are separated by a thinshim or insert 27 of nonmagnetic material.

The parts which serve to mount and retain the transducer units, are ineifect interlocked with portions of the member 16. Thus for the mountingof each transducer unit, a marginal portion of the member 16 is providedwith a recess 28. The surfaces 29 defining sides of this recess areformed on a circle which extends slightly beyond the periphery 30 of themember 16, as shown in FIGURES 8, 9, 10, and 11. The recess 28 isadapted to accommodate the circularly contoured (i.e., disc-like)mounting element 31. The inner face of each element 31 is provided withgrooves 32 disposed in the form of a V, which accommodate the polepieces 24. Another and deeper circularly contoured recess 33 isdimensioned to accommodate the magnetic core 21. Immediately beneath thecore 21 there is a compressible member 34, formed of suitable plasticmaterial or composition, and which serves in the final assembly tomaintain pressure contact between the core and the pole pieces 24. Oneterminal of the coil 23 is grounded, and the other is connected to aterminal screw 36 that is carried by the insulating bushing 37. FIGURES8 and 12 shows a lo cating pin 38 carried by member 16, and accommodatedwithin the slot 39 formed on the inner side of element 31. Dependingsomewhat upon methods used for assembly, this pin may or may not beomitted.

During assembly care is taken to obtain accurate location of the poletips, whereby the angular spacing between the gaps 27 is uniform.However, it has been found impractical if not impossible to manufacturethe head assemblies with such a degree of precision that the angularspacing between gaps is exactly uniform and identical for each assembly.

To provide means for precise adjustments the member 16 is divided into aplurality of connected sectors, with each sector serving to mount one ofthe transducer units. Thus as shown in FIGURE 6 radially extending slots41 are provided intermediate the transducer units, and these slotsextend from the outer periphery to points near the central opening 17.For convenience and to relieve stress, the inner ends of these slots mayterminate in the openings 42, which may be used for the attachment ofasso- 4 ciated parts. Each slot is interrupted by a threaded taperedopening 43 which accommodates an adjusting screw 44. All of theadjusting screws are tapered whereby when a screw is advancedsufliciently far it causes slight spreading of the associated slot.

Various techniques can be employed for assembling the transducer unitsupon the member 16, and for securing the necessary precise positioningof the parts during various stages of manufacture. While the transducerunits are being assembled and located, the adjusting screws 44 are leftrelatively loose whereby they do not affect the relative angular spacingbetween the sectors. By means of suitable precision fixtures andinstruments, the gaps 27 of the transducer units are located asprecisely as possible relative to each other, to provide uniformspacing. Assuming the use of four transducer units, the gaps 27 arelocated apart. When the parts of a transducer unit are assembled in theposition desired, suitable means such as selfsetting resin of the epoxytype can be applied to bond the elements 31 to the member 16. The tips26 are also accurately ground to protrude the desired amount from theperiphery of the assembly, whereby all of the tips lie in a common sweepcircle. Thereafter the head assembly is placed in a video recording and/or reproducing machine, and employed for the reproduction of signalinformation from a standard recorded tape made with a head havingaccurate redundant adjustment between the gaps of the transducer units.The reproduced picture is observed and the extent of shifting ofhorizontal bands is noted. The operator now makes adjustments of thescrews 44 whereby the angular relationship between adjacent transducerunits is adjusted to the extent necessary to avoid picture distortion.The head is now properly adjusted for precise recording and/ or playbackoperations.

As shown in FIGURE 1, the head assembly 10 (just described) isassociated with a suitable slip ring assembly 47, whereby the terminalleads number 1 to 4 inclusive make connection with the ungroundedterminals of each of the transducer windings. Lead 5 and the slip ringconnected thereto provides a ground connection. The inner rotatable partof this slip ring assembly can be attached to the spider 48, and thisspider, together with the head member 16, and a driving hub 49 on themotor shaft, all clamped together by means of screws 50. A part of thehead periphery can be enclosed by the housing 51 (FIGURES 1 and 3) whichis carried by the base 13. The immediately adjacent housing part 52 canserve to mount and enclose the photoelectric tube 53 and the small lamp54, (shown in FIGURE 4), together with means for focusing the same uponthe periphery of a ring 55 on the hub 49. One portion of this peripherycan be darkened, and the remainder light reflecting,- whereby circuitryconnected to the photoelectric tube serves to generate pulses insynchronism with rotation of the head. Such pulses can be used for motorcontrol and synchronizing operations.

The tape guide 12 is provided with an arcuate inner face 56 whichembraces a portion of the periphery of the head. It is fixed to an arm57 which overlies the base 13, and which has its one end removablyattached to the pivot pin 58. This is carried by the bearing assembly59, and is shown releasably attached to the arm by the set screw 61. Theguide member 12 together with arm 57 are movable between limitingpositions, in one of which the guide member is retracted with respect tothe head whereby a tape is free to move past the guide member withoutbeing contacted by the transducer units, and in the other of which theguide is advanced relative to the head whereby the tape is held incontact with the transducer units.

Means is provided whereby the guide member is normally urged toward thehead. Thus a lever 62 is urged by compression spring 63, and is securedto the base 13 by the pivot pin 64. The roller 65 carried by one end ofthis lever engages an inclined cam face 66 formed on the .5 extension 67of the arm 57. By virtue of the cam face 66 and roller 65, the force ofspring 63 normally serves to yieldably urge the arm and the guide towardthe head and downwardly toward the base.

A stop screw 69 carried by the extension 67 of arm 57 engages a bearingassembly 71 carried by shaft 72. An arm 73 has its one end secured toshaft 72, and its other end is disposed to engage the adjustable stopscrew 74. Suitable motor means such as a solenoid 76 of the rotary typeis mounted below the base 13, and has its shaft coupled to a shaft 72that is journalled within the base, and which has the stub shaft 75eccentrically attached to the same. When the solenoid 76 is energized,the tape guide member 12 is in its advanced position, and arm 73 isagainst the stop 74. When solenoid 76 is not energized, as for taperewind operations, arm 73 is rotated a limited amount in acounterclockwise direction as viewed in FIGURE 1, whereby theeccentricity between shafts 72 and 75 causes displacement of arm 57,with the result that the guide member is retracted for free movement ofthe tape.

When it is desired to remove the guide together with arm 57 from themachine, the operator operates the lever 62 to compress spring 63sufficiently far to release the roller 65 with respect to the cam face66. Thereafter the arm 57 can be removed together with the guide.

It is desirable to steady the arm 57 by supplemental guide means nearits free end. It is also desirable to pro vide means for adjusting thevertical height of said guide means whereby the height of the arm 57 maybe controlled. For this purpose a slide bar assembly 81 is fitted withinan accommodating slot formed in the base 13. The slide bar assembly hasone of its ends fixedly secured to the base by means of a bolt 83. Theother end is adjustably secured to the base 13 by a bolt 84 which has adifferential thread arrangement for adjusting the height of this end ofthe slide bar assembly. Vertical movement of the slide bar serves tovertically position the arm 57 which rests thereon. Teflon inserts 82(FIGURE are secured to the slide bar for the purpose of providing smoothlow friction suspension points on which the arm can move.

The arcuate surface 56 of the guide member 12 is preferably providedwith an arrangement of grooving or recesses as shown in FIGURE 1. Thus agroove 86 is formed in a plane corresponding to the plane of rotation ofthe transducer units. Additional grooves 87 are pro-.- vided adjacentthe sides of the groove 8-6, and are adapted to be connected by flexibletube 88 to a source of suction. Suction applied during normal operation,that is, during recording and/ or playback operations, serves to retainthe exterior side of the tape in intimate contact with the guidesurface. As shown in FIGURE 3 an abutment 89 is provided at the lowerend of the guide member, and serves to engage one edge of the tape. Itis assumed in this instance that the head rotates in a counterclockwisedirection as viewed in FIGURE 3.

It is desirable to provide pneumatic cooling for the motor. Thus a duct91 connects with one end of the motor housing 92 and is connected to asuitable source of suction whereby cooling air is continuously drawnthrough the motor windings. It is also desirable to provide pneumaticmeans for withdrawing dust from the tape and from the vicinity of therotating head. For this purpose the housing part 51 is hollow and isconnected to a similar suction duct 93, whereby air is continuouslydrawn from the region of contact between the head and the tape, thusremoving dust or other fine particles.

Operation of the complete transducer apparatus will be apparent from theforegoing. FIGURE 13 schematically illustrates how tape is applied tothe guide means 12, and is driven by a capstan drive. During normalrecording and/or playback operations, the guide is advanced toward thehead, the precise position in this instance being determined by thesetting of stop screw 74.

From time to time this screw can be adjusted to compensate for wear ofthe transducer tips. Such adjust- ,ments serve to adjust the contactpressure between the tape and the transducer tips. During fast forwardor tape rewind operations, the solenoid 76 is de-energized to retractthe guide member, whereby the tape is free to move without contactingthe transducer units.

The particular head construction described makes possible economies inmanufacture, while at the same time permitting high precision withrespect to the location of the gaps of the transducer units. By means ofthe features described, it is possible to build and assemble the headwithin reasonable mechanical tolerances, and thereafter effectadjustments which make for exact precision: The use of such a headobviates the use of delay lines for both recording and/ or playbackoperations.

What is claimed is:

1. In tape transducing apparatus, a plurality of transducer units, arotary drum serving to mount said units for movement on a predeterminedcircular path; means for positioning said tape with the entire width ofone side thereof lying on said path so that said entire width of saidone side of said tape is swept by each of said units on each revolutionthereof; said means including arcuate guide means adapted to engage theopposite side of said tape across said entire width of said tape on saidpath, whereby a portion of the tape is cylindrically curved andpresented for contact with the tips of the transducer units, meansserving to carry said guide means for movement of the same toward andaway from said drum with the center of curvature of said arcuate guidemoving parallel to an axial plane of said drum, said movement of saidguide means being toward and away from said drum between two limitingpositions, in one of which the curved portion of the tape is presentedfor operating contact with said transducer units and in the other ofwhich the tape is out of contact with said transducer units and is freeto move in the direction of its length, and means for shifting saidguide member from one of said limiting positions to the other.

2. Apparatus as in claim 1 in which said first named limiting positionof the guide means is adjustable.

3. In tape transducing apparatus, a plurality of transducer units, abase, rotatable transducer mounting drum carried by the base, saidtransducer units being carried by said mounting drum for movement on apredetermined arcuate path, means for positioning said tape with theentire width of one side thereof lying on said path so that said entirewidth of said one side of said tape is swept by each of said units oneach passage thereof, said means including arcuate tape engaging andguiding means adapted to engage the opposite side of said tape acrosssaid entire width of said tape on said path and to guide a cylindricallycurved length of said tape for movement in proximity with said arcuatepath of the transducer units, means serving to support said guide meanson said base for movement of the guide means with the center of arcuatecurvature thereof moving parallel to an axial plane of said drum andbetween one limiting position in which the guide means presents thecylindrically curved tape portion for operating contact with the tipends of the transducer units and in the other limiting position the tapeis retracted from such contact and is free to move lengthwise, means forshifting said guide means between said limiting positions, and means foradjusting the distance between said guide means and the axis of rotationof the transducer units for said first limiting position, said adjustingmeans serving to compensate for wear of said units with correspondingchange in sweep radius.

4. Apparatus as in claim 3 in which the means serving to support theguide means comprises an arm having its one end pivotally connected tothe base for movement of the arm toward or away from said axis ofrotation 7 and its other end serving to mount the arcuate guide means.

5. In the tape transducing apparatus, a rotary drum, transducing meanscarried by the drum for movement on a predetermined arcuate path, meansfor causing one side of said tape to engage said transducing means onlyon said path, said means including an arcuate guide member adapted toengage the opposite side of said tape along the entire length of saidarcuate path and to guide and present a cylindrically bent portion ofsaid tape for contact with the transducing means whereby the transducingmeans sweeps along said path across the tape, a base, an arm having oneend of the same pivotally attached to the base and its other end securedto the guide member, the axis of the pivotal connection being at rightangles to the axis of rotation of the drum whereby swinging movement ofthe arm moves the guide toward or away adjusting said last named guidemeans to thereby adjust the position of the arm in a directionperpendicular to the plane of said swinging movement.

References Cited by the Examiner UNITED STATES PATENTS 2,912,518 11/59Maxey 179100.2 3,020,356 2/62 Barry 179-1002 BERNARD KONICK, PrimaryExaminer.

IRVING L. SRAGOW, Examiner.

1. IN TAPE TRANSDUCING APPARATUS, A PLURALITY OF TRANSDUCER UNITS, AROTARY DRUM SERVING TO MOUNT SAID UNITS FOR MOVEMENT ON A PREDETERMINEDCIRCULAR PATH; MEANS FOR POSITIONING SAID TAPE WITH THE ENTIRE WIDTH OFONE SIDE THEREOF LYING ON SAID PATH SO THAT SAID ENTIRE WIDTH OF SAIDONE SIDE OF SAID TAPE IS SWEPT BY EACH OF SAID UNITS ON EACH REVOLUTIONTHEREOF; SAID MEANS INCLUDING ARCUATE GUIDE MEANS ADAPTED TO ENGAGE THEOPPOSITE SIDE OF SAID TAPE ACROSS SAID ENTIRE WIDTH OF SAID TAPE ON SAIDPATH, WHEREBY A PORTION OF THE TAPE IS CYLINDRICALLY CURVED ANDPRESENTED FOR CONTACT WITH THE TIPS OF THE TRANSDUCER UNITS, MEANSSERVING TO CARRY SAID GUIDE MEANS FOR MOVEMENT OF THE SAME TOWARD ANDAWAY FROM SAID DRUM WITH THE CENTER OF CURVATURE OF SAID ARCUATE GUIDEMOVING PARALLEL TO AN ACIAL PLANE OF SAID DRUM, SAID MOVEMENT OF SAIDGUIDE MEANS BEING TOWARD AND AWAY FROM SAID DRUM BETWEEN TWO LIMITINGPOSITIONS, IN ONE OF WHICH THE CURVED PORTION OF THE TAPE IS PRESENTEDFOR OPERATING CONTACT WITH SAID TRANSDUCER UNITS AND IN THE OTHER OFWHICH THE TAPE IS OUT OF CONTACT WITH SAID TRANSDUCER UNITS AND IS FREETO MOVE IN THE DIRECTION OF ITS LENGTH, AND MEANS FOR SHIFTING SAIDGUIDE MEMBER FROM ONE OF SAID LIMITING POSITIONS TO THE OTHER.